In electronics systems, electronic components such as printed circuit boards are often housed in circuit modules (or cages) having holes in their top and bottom portions to allow for air circulation around the components for cooling purposes. The modules are often arranged vertically, side-by-side, between shelves of a card cage, all of which being housed within a cabinet or chassis.
Often, electronics systems are cooled by fans which are placed in a permanent, fixed location inside the cabinet of the electronics system.
The prior art reveals complicated techniques to help improve the evenness of airflow through electronics systems. For example, UK patent application 2,197,536, in the name of STC plc and published on May 18, 1988, describes an equipment cabinet having a central chimney or spine in the centre, surrounded by electronic circuit units. The units are stacked vertically. By a complicated arrangement of air intake areas, baffles, and inlets into the chimney, the cabinet helps to distribute airflow through the units. However, this invention requires a specially built cabinet and chimney structure and requires the ability to stack electronic component units vertically, which, given space constraints, may not be possible or desirable in many electronics systems.
A simpler device for improving airflow through circuit modules is described in U.S. Pat. No. 4,860,163 which was issued to Sarath in 1989. The Sarath device describes a cabinet for holding circuit modules, with a fan, centrally located, drawing air from one end of the cabinet. There is a wall at one end of the modules closest to the fan preventing air from flowing directly from the modules to the fan. Instead, air must flow around the wall to reach the fan. To further improve air flow distribution, baffles are placed along a portion of the sides of the cabinet to force air to flow over at least a portion of the modules. For this device to help improve the evenness of air flow, it appears necessary that the fan be relatively centrally located. If, as in many electronics systems, the fan is not centrally located, air flow will not be significantly improved, if at all, in portions of the modules remote from the fan.
In electronic systems, modules are often housed vertically in a cabinet. The modules typically have a faceplate at their forward portion and connectors at their rear portion for connection to a backplane. In such systems, often at least one fan is located above and at or near the rear portion of the modules (at or near the backplane), which draws air from below the forward portion of the modules. Accordingly, without a device to help evenly distribute air flow, the air will tend to travel in a relatively straight line defining a diagonal between the lower forward portion of the modules to the upper rear portion of the module, thereby avoiding to a significant extent, areas of the modules outside the diagonal.
For air flow distribution outside the above-described diagonal, filters, placed below the modules, have helped to an extent. Because a filter creates an obstacle to air flow, a filter helps to distribute the air entering the modules over a greater proportion of the surface area of the bottom of each module. As a result, the use of a filter helps improve air flow distribution through the modules. However, filters add to the cost of such systems and require periodic maintenance (to either clean the filters or to replace them when they become "dirty").
In the absence of a filter, honeycomb structures have been used to help air flow distribution. Although such honeycomb structures improve airflow, they are relatively expensive to manufacture and they do not distribute air over the surface area of the modules as evenly as is desirable.